how does multiplayer work?

[Apex Trill]

is there split screen or local coop? and how does the online portion work... pvp?

[Nogardust]

This game can be played ONLY with two people, each owning a copy of the game. You progress the story simultaniously, but at different places/points of view. Have you ever tried explaining to someone over the phone how to fix a broken printer or something? This is what you're going to do, basically.
This game is actually the third in series (We Were Here -> We Were Here Too -> We Were Here Together), all of them are really great and the first one is completely free, so you may as well just try We Were Here first.

[Apex Trill]

nice, thanks